GitHub: size of remote file is not known

[Chris]

I don't use Github. So I'm not familiar with their service(s).
But ports using source fetched from them always return:
size of remote file is not known
Is it that their servers simply refuse to return size/content-length
or is this something else?
I can see where this might turn into a problem for those attempting
to build ports on a system with limited resources -- especially
during a meta-port build, and even more so for newcomers.

Is anyone familiar with why this is so? I'd like to change this.

Thanks!

--Chris